Differential duplex telegraph repeater



April 24, 1926. I 1,666,965

J. HERMAN DIFFERENTIAL DUPLEX TELEGRAPH REPEATER Filed June 26, 1926 AAIAAAAAAAVA mORNE Y Patented Apr. 24, 1928.

A UNITED sT Tss 1,666,965 PATENT OFFICE.

JOSEPH HERE, OF NEW YORK, 11'. Y., AB SIGNOB TO AMERICAN TILIPKOII LID TELEGRAPH COMPANY, A CORPORATION 01' NEW YORK.

DIFFERENTIAL DUPLEX TILEGRAIE mum Application fled June 28, 1986. Serial No. 118,688.

This invention relates to grounded direct current telegraph systems, and more particularly to the differential duplex repeater circuits employed in such systems.

The object of the invention is to provide improved arrangements for reducing interference with telegraph systems from alternating current power transmission systems.

It has been the practice heretofore to employ resonant shunts connected across the receiving relay windin of telegraph systems of the class to which the invention relates. These shunt circuits are tuned to the frequency of the interfering power currents, offering a low impedance to these currents and a high impedance to the signaling currents.

In accordance with the invention described hereinafter, I rovide a novel circuit arrangement inclu ing a resonant shunt which is rendered highly protective against interfering power currents, as described more fully below.

The accompanying drawing shows in diagrammatic form a differential duplex telegraph repeater circuit arranged according to my invention. The telegraph line, the balancing artificial line, the sending relay and the receiving relay are elements old and well understood in the art.

The receiving relay includes the winding W in series with the real line, and the winding W in series with the artificial line. The" resonant shunt consists of the inductance L and the capacity C. It has been the usual practice to connect such a resonant shunt directly across the terminals of the receiving relay. With such an arran ement, the amount of protection afi'or ed against interfering currents depends upon the relative impedances'of the shunt and of the receiving relay. Since the resonant shunt always has an appreciable resistance even though it is accurately tuned to the frequency of the interfering current, it is not possible with such an arrangement to exclude all interfering current from the relay. By arranging the repeater circuits according to m invention, this objection is overcome an better protection afforded against interfering currents, since the residual interfering currents may be balanced out.

Let it be assumed that the artificial line offers a high impedance in comparison with ceiving relay. balance of t e repeater system is upset b an the direct current resistance of the receiving relay winding W added to the resistance to ground through the batteries associated with the sending relay. With this assumption, the presence of the artificial line may, for the purpose of the first part of this discussion,

e neglected. The lnterfering alternating 'current flowing into the repeater from the sistance R is chosen equal to R The insertion in the circuit of this resistance R Wlll cause the interfering current to divide equally between the two windings of the re- The result is that the duplex amount corres onding to the effect 0 resistance R ccordingly, a resistance R equal to R must be added to the artificial km. with this arrangement, the only duplex unbalance existing will be a very slight one due to the un metrical connection of the resonant shunt C with respect to the reslstances R and R and it can be disregarded.

It was assumed above that the artificial line ofl'ered a high impedance. If, however, the artificial line has a comparatively small Impedance to the interfering currents, its presence must be taken into consideration and. compensation provided. The resistance R must be made lar'ger than the effective resistance R of the resonant shunt whereby a larger amount of current will be caused to flow through the resonant shunt than through the resistance 3,. Part of this current will flow into the artificial line, and the balance through the relay winding W Accordingly, by proper adjustment of the value of resistance R,, the currents flowing in the two windings W and W, can be made approximately equal, in order to produce neutralization.

It is thus seen that applicants simple resonant shunt arrangement permits of the balancing out of the residual interfering currents usually present, and afiords suitable protection against interference with the a 2. In a balanced differential duplex tele- 2 repeater from power currents in the telegraph line. 7

What is claimed is:

1. In a differential duplex telegraph repeater system, a line, an artificial line, a sendin relay, a receiving rela having a first wmding in series with sai line and a second winding in series with said artificial line, a shunt path between said line and said artificial line, said shunt path including an inductance and a capacit of such values that they form a tuned circuit resonant at the frequencies of interfering alternating currents in the line, a first resistance in'series with the first winding of the receiving relay, and a second resistance in the artificial line, said first resistance being of such a value that the interfering alternating currents will divide between the two windings of the receiving relay, having no effect upon said relay, and said second resistance being of such a value that a duplex balance of the systemis maintained.

graph repeater system, a line, an artificial line, a sending relay, a receiving rela having a first winding in series with saidline and a second winding in series with said artificial line, a shunt path between said line and said artificial line, said shunt path including an inductance and a capacity of such values that they form a tuned circuit resonant at the frequencies of interfering alternating currents in the line, a resistance in series with the first winding of the receiving relay, and a resistance in the artificial line, said resistances being of such values that the interfering alternating currents will divide between the windings of the receiving relay, having no effect upon 7 the operation of sald relay, and the duplex balance of the system is maintained.

In testimony whereof, I have signed my name to this specification this 24th day of June 1926.

JOSEPH HERMAN. 

